Silica glass



Nov. 17, 1925- i... B. MILLER sILlcA GLASS original Filed April '1, 1921 hyp 1 l l' --InVey'tC-.orz

Levi' B" Miller?` His;

' The present1nventionfconstitutesan apr paratus'- .adapted for the fabrication .of

Patented Nov. 1 7, 1925.

UNITED. vs 'rrvrr-vs nnvI B. nimma, oFLYNN, MAssAcHUsnrrs, AssIeNon -ro GENERAL COMPANY, A CORPORATION or NEW .rome

-, y 1,562,115 11.1.'1'15N'1r orales..

ELECTBIG,

sILIcA eLAss originar www ma Aprn 1, 1921, smal No.

i -TogaZZ'wlw-m it may concer/1.'. 2 -Be it known that I, LEVI B. MILLER, a citizenI of' the United States, Vresiding at Lynn, in the ycounty of Essex, State of Masifsachusetts, have invented 4certain new and vluseful Improvements in VSilica Glass (divi sion of m application, Seria1-No.`457,660,` Apri 1', 1921), of which the following ,As described in Patent No. 1,536,221 of 'l5 May 5,1925, granted to Phili K. Devers,

transparentsilica glass may made`-.byI fusing quartz, for other suitable -formI vof ure silica, in s. vacuum, andthen compresslng themass while plastic to' substantially 50 eliminate the 'cavities which' are formed in" the fusion even when -the silica is fused'in a vacuum;

vitreous silica whereby'vac'uumdusedsilica is mouldedin the presence ofgas under sub-v .stantial pressure to a desired form,l for-'exthe plastic glass from ample, b extrudin lrectly mto the atmosthe heating zone 5 0 p'here..v Thepresent invention comprises 'in particular a' furnace .for carrying 'foutthe extrusion process which is claimed in my co endin `divisionalapplication Serial No.

457,660, led April 1, 1921. The n vel fea- 4 35 `tures of. my invention will be" pointed out with particularity in vthe appended claims.

Among the advantages secured byv'my invention are the easy accessibility of the heat-- ing zone, the delivery -o`f the shaped' silica 4' 1 0 'info the open where it may bechilled to prevent deformation, the utilization of a cheap material such as graphite, asa container for .7' .fusions of silica,'and the' provision of `'api paratus for producing directly from plastic Y silica, shaped articles, such as tubes, which are transparent and substantially free from bubbles. .'For a complete understanding 'of my invention, reference may'behad to the followingdescriptien taken in connection with the' accompanying drawings in whichFg'. 1 is avei'tical section of a'furnace having a heating chamber open to the atmosphere and being. provided with means for extruding .'his furnace provides a heating'- space .whlch' 1s o en to the atmosphereso that the 457,eeo. -mvidea and um appuuuonfnea v1.1mm;

13,1e2s. serial No. 618,859.

vacuum-fused quarta under pressure; Figs@ and 3 'are detail sectional views. lof e die suitable 'for ex'truding tubes of quartz.

In' carrying ont my invention as a prelinii-' nary step, a-suitable form of silica, for 'ex'- ample, crystalline-quartz, is fused in a u vacuum' 1nA accordance with thepf` are described in theabove Devers patent. The' resulting slugef vvitreouaor glassy silica. is 'transferred to afurnace such as own in vitreous' si ica in'its'plastic state is net only lacted upon .by atmospheric pressure, buty can -be extruded :through afdischarge rt at the 70 lbottom of the furnace into a'wor ing space beneaththe furnace,..thereby aiding the o -crater when 'carryin outtheprocess. e furnace comprises a eater 15,. which for V15x- ...ample, may consist of a carbon tube eennected' aj-t opposite ends to water cooled terminals 1 6, 17, towhichare connected electric conductors 1 8, 19. Carbon or graphite rin 20,21, preferably are placed between the tu 115 andthe terminals 16, 17, which may consist of' copper, The carbon. tube is sur-.-y rounded by a packing ofcharcoal or other suitable heat insulating material 'contained' within. a receptacle '22,'. which conveniently" consists of asbestos. The fu-rnace'is supported at a considerable height upon a 'platfenn 2 3, theup ryend of the furnace as we11=asjthe platieerm 23 being connected to u 'rights' 24. Within the heater4 `15 is a 'grap itecrucible 25 which v-projects through the up r part of the furnace. The interior of t el crucible 25 coinmunieates withthe heating .space'throu h la vent hole 26.' The space betweent e gra hit'e, Crucible 25 and the heater tube-15 is-c osedby a cap '27 consisti or other Suitable material suita ly connected to the ring 21 by aplate 28 with screws29, asbestos insulating-rings being rovided both between the cap 27 and the tu 15, an'dbei tween the cap 27 and the plate 28.- Fitting.. into thegraphite crucible. 15 isa graphite 'ff piston 30 conn c tedvv to a rod 31 at the u er end of which scrried a `weight 32..v islx weight may be 'counterbalanced by ,another weight 33 (when in the position shown by4 dotted lines)'. The two weights are'attached -to'a flexible cable 34 passing 'over the pulleys of graphite vopening or a die.

lil

35, 55". As shown in Fig. Lit/hre bottom ofy the crucihlefis"provided with an extrusion l as will be hereinafter more fully explained.

Before the furnace is put into operation and before a charge of silica is placed therein the parts of the furnace subject to heating, which consist entirely-of carbon, are purified by making a blanhv run at or slight-, ly above the operating temperature. Pref erably the graphite Crucible, the piston and the die if used as later described, are tired in a vacuum to about 2000o C. or over, before assembling the furnace. By thus volatilizing mineral matter from the crucible and other Ifurnace members which i.comeinto di-. rect v'contact ivith the fused silica or arey located closely adjacent'the silica charge, it isgpossible to obtain a clear, .uncontaminated fusion even at the high ytemperatures. employed. Former attempts to .fuse silica' in carbon containers resulted in a cloudy or` even opaque product. I ,liave found that this contamination of the silica was not` due to chemical combinationofthe silica and the carbon, but was' due to mineral impurities `:in the carbon which vdissolved 1n the silica. Somechemical reaction between thev silica Vandy the, carbon appears `to occur at high-temperature and carbon monoxide gas is produced which soon fills up the furnace, interior land prevents access of air. In any event, pure clear vitreous silica maybe produced in apparatus prepared in accordance with my invention.

-When the furnace partsy have `been purified, a mass of vacuum-fused silica prepared asy above described, is placed in the Crucible and the'jfurnace is brought, up to the operating temperature of aboutilZOo'C.- As the space'within the heater tubel'is closed at the top, air is soonexeluded by the heated carbon monoxide vgas generated within the furnace Pressure is exerted upon the mass, of silica' when plastic, forL example, by litt.v ing the'coiinterbalancing Weight 33 and placing it upon hook 37 as shown in'full lines),

' thereby causing the full force ofthe weight 32, which may Weigh 30 to 35 fpoundspor more,'to be exerted through the graphite piston through themass of silica, the cross-scction ofwhieh'may consist of aboutil to3 sq. i in.l As already indicated, when the temperature of ythe silica glass reaches about i700 to *1750"I C. the pressure exerted thereupon very largely, or even entirely, eliminates bubbles and produces mass. 'y

I prefer, in accordance'wi'th my invention, to utilize pressure upon the fused silica glass, not onlyvto eliminate bubbles, but to shape the glass into suitable form such asv canelor tubes. its shown in Fig. l, the bottom of 'the crucible`25 is provided with a perforation through which maybe-extruded a clear glassy4 a rod or cane of silica glass 40, asshown in the drawing. In order to prevent deformation of the cane, it is preferably extruded di-vv rectly into a cooling liquid, for example, Water,- contained in the receptacle 41. The Water vnot only cools the cane but also counterbalances the Weight of the cane in part thereby preventing the weight of the cane extruded from the crucible from'acting cumulatively upon the still plastic silica as it issues from the Crucible, or in other Words, to prevent the weight of the suspended mass from ydecreasing the diameter of the extruded cane.

I have shown in Figs. 2 and 3 a suitable dic Lfor making quartz tubing. In this case the bottom of the Crucible is provided with van annular opening. The core 42, consisting ofy graphite, is connected to the side of the crucible 25 by a right-angled offset section 43 removed a suiiicient distaneefrom the end of the tube to permit the plastic quartz to flow past the section 43 and then to reunite upon entering the throat of the cir- .eular extrusion opening between the core 42 and the reinforced end Wall 44 ofthe crucible. Preferably the core 42 is made tubular and a hollow core communicates with the atmosphere to permit of the discharge of vgases generated inv the interior of the extruded tube 45, thereby maintaining the 'tube at substantially uniform diameter.

. What I clainras new and desire to secure by Letters Patent of the United States, is

1. An electric furnace adapted for shaping plastic silica which comprises a container providing a vertical heating zone having a discharge port located at its lower end, an electric heater therefor, a refractory crucible supported in said heating zone and having a die aligned with said. discharge. port to permit of the extrusion of material therethrough and means for extruding a chargel from said refractory container.

l2. An electricv furnace comprising a container having an opening atthe bottom, a refractory crucihle supported therein and provided withan annular yorifice for the discharge -of material, means for supporting said container at the upper end on y with said oriticeinline yWith said opening to permit expulsion ofl material `froin said oritice, means for heating sa'idpcrucible by'Y radiation, and means for expelling a chargeY in said container through said orifice.

3. Annapparatus for shaping silica glass comprising a receptacle for s aidilgl'ass prol vided with an extrusion opening, means for-r heating said glass to the plastic state and a receptacle containing abody cated to' receive extruded silica.

4. An apparatus for making quartz tub# ing comprising a refractory Crucible having a die opening, a core located in'said opening and supported at a place removed from 130 vsis' los i 11i;l y j Said opening, said core loein provided with e duet communicatin wit the exterior, means for heating sai cruoible and means for subjecting a charge in saidl Crucible to pressure.

v for heating a charge in said Crucible and A, for applyingpressure upon said piston to extrude the charge when in a. plastic condition through said die'opening.

mea-ns v5 6. An eieetric furnace adapted for theextrusion ofvfused quartzeomprising e tubular I refratory heater, electrodes at opposite ems of. said heater, a closure for the upper end of said heater the opposite end being opten,

a refractory Crucible having a die opening 2o and being supported from said closure, an elevatedupport for said heater providing a working space beneath said heaterv and means-for extruding a charge in said creci ble through the die oieningmm the working 2o space beneath said eate In witness whereof, I have hereunto set my hand this 5th day of February, 1923.

LEVI B. MILLER. 

